This invention relates to conveyor drive systems and, more particularly, to conveyor drive sprockets formed of plastic materials.
For a number of reasons, including cost, weight, durability and ease of manufacture, conveyor drive sprockets can advantageously be formed of a variety of plastic materials. One drawback to the use of such materials, however, is that plastics generally have lower shear and torsional strengths than most metals. Material failure at the interface between a conveyor sprocket and a powered drive shaft on which it is mounted is often the limiting factor in defining the maximum drive capacity of the sprocket. The problem of limited plastic strength is particularly acute when conveyor sprockets are required to move axially on a drive shaft as, for example, to accommodate temperature changes. Such sprockets cannot be locked firmly to the drive shaft.
In U.S. Pat. No. 3,724,285 (reissued as Re. No. 30,341) and U.S. Pat. No. 4,865,183, axially movable plastic conveyor sprockets are mounted on drive shafts of substantially square cross section. The relatively large dimensions and the square comers of the driven shafts effectively transfer torque to the conveyor sprockets without concentrating forces and without thereby causing material failure in small areas of the sprockets. Although effective, square drive shafts have certain drawbacks, particularly in such areas as manufacture and mounting for rotation. Such sprockets are not usable with round shafts, which are considerably simpler to manufacture and mount than square shafts.